Gah! I've got the same problem - colour picker returning dark values. Not sure when it started but had it for a while. I'm on R20 on Mac, are as you.
EDIT: I just switched to Linear workflow and restarted, and the problem seems to have corrected itself!

I switched form LW3D o C4D with release R14 I think. Had a good deal on Studio bundle and have paid the yearly MSA to stay current. The last few years I've done it but not massively benefited from the new features – apart from a bit of novelly interest and some fun tools. I can afford to pay the MSA, but it's getting tougher to justify as I'm not a professional artist – although I wish I could get some CG work.
Persanally I think the MSA is a a tad on the high side, but I loathe Adobe's rental system, so am okay with the current yearly upgrade. I will say that with the likes of Blender 2.8 now around, MAXON really has to put some effort into making the app better. It feels like it's falling behind in some areas, like display, handling of large datasets, rendering speed (not everyone wants a third-party renderer bolted on, although it now seems inevitable). But I do like C4D and am keen to see how it will evolve...

You'll need to get to grips with the Layer shader. This creates a stack system where you can use images, effects and shaders to add/multiply/subtract and mask other layers. Once you get your head round it, it's pretty logical. You can apply the Layer shader at any time, and it'll put whatever is in your texture slot into a layer. You then add an image, shader, effect or a folder from the buttons. To edit a layer, click on the small square icon next to its name. Click and a hold that icon to reorder layers. Let us know how you get on!